Antenna for short and ultra-short waves



Jul 25, 1933. w. HAHNEMANN 1,920,155

ANTENNA FOR SHORT AND ULTRA-SHORT WAVES Filed June 20. 1930 Patented July 25,1933

. B A-I EfNl'll o EFicEf WALTER HAHNEMANN, OF BERLIN-MARIENFELDE, GERMANY, ASSIGNOR To C. LORENZ AKEIJIENGrESI-ELLSGHAF'JI, OF BERLIN-TEMPELHOF, GERMANY ANTENNA r03 SHORT AND ULTRA-SHORT WAVES Application filed June 20, 1930, Serial No. 462,487, and in Germany October 30, 1929.

As is well known, a directed reception of short and ultra-short waves by means of a frame antenna is not possible according to the present methods. This fact is to be at- I tributed to the circumstance, that the laws otherwise recognized in the high frequency art, have not been considered in dimensioning the frame-antennae used. It is known, that with a mean wave-length of for instance 400 metres usually a frame of about from 40 to centimetres side length will be employed. With longer waves relatively larger frames are used, which with commercial stations in particular possess a side length of several metres. The tests mentioned and carried out with the available frames for mean wave lengths for the'directed reception of short waves, showed that a directed reception was not possible.

The conviction, that a directed; reception of such waves is not possible at all, must be attributed to said fact. By virtue of oer tain properties, short and ultra-short waves persist in covering much greater distances than do the waves employed in long wave transmission. Furthermore, short waves are not deviated from their straight line course as easilyas are long waves. Because of these properties the shorter waves are particularly useful in transmitting direction signals to ships and airplanes. Commercial short wave sets now operate successfully on from about 25 down to-16 meter wavenected with the earth.

lengths. Thus it becomesimportantthat an antenna arrangement for short wave reception having gooddirectivity is found for use in short wave radio direction finders.

According to this invention, the dimensions of the frame or loop of such an antenna arrangement must be so chosen, that the side length is very small in comparison with the wave length, amounting to a maximum of one-tenth of the wave-length. Besides, the distance of the frame from the earth potential must be as large as possible, but at least one-half of the wave-length.

One mode of construction of the arrangement according to the invention is shown on the drawing by way of example.

That proportions of the dimensions are concerned which are not customary nowadays, follows from the accompanying drawing in particular. The frame R is connected by way of a supply lead V of energy with the high frequency initial circuit of the apparatus G. The side length of the frame is to be one-tenth of the wave-length at the most, while the distance a amounts to at least one-half of the wave-length. This unusually great distance must be chosen, so that the capacity between the frame and the apparatus, which obviously must be con.-

sidered also as earth potential, remains sufficiently small. This condition in particular is not observed in the former frames nor was it necessary there to observe such condltlons, since the influence of the capacity within the range of mean and longwaves is not decisive owing to the other dimensions of the high frequency circuits. The supply line for the energy is, in order to ensure a symmetry of the conditions, designed particularly as concentric conductor surrounded by a hollow conductor, or in the form of two conductors arranged within a metal hose or the like. For maintaining the conditions of symmetry it is also of advantage, to connect with the earththe secondary coil of the coupling device in the center, or to choose as coupling device some capacities, which on the one hand are connected tot-he supply line for the energy and on the other hand their center point is con- 2. An antenna arrangement for directive I Lin oeived, and an antenna lead comprising two conductors arranged Within a conducting shield and adapted to efl'ect a connection between the loop and an apparatus connected to earth potential, said lead having an effective vertical length of not less than half the length of the Wave tofbe received.

WALTER HAHNEMANN.

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